The field of art to which this invention pertains is the hydrocracking of a hydrocarbonaceous feedstock. Petroleum refiners often produce desirable products such as turbine fuel, diesel fuel and other products known as middle distillates as well as lower boiling hydrocarbonaceous liquids such as naphtha and gasoline by hydrocracking a hydrocarbon feedstock derived from crude oil, for example. Feedstocks most often subjected to hydrocracking are gas oils and heavy gas oils recovered from crude oil by distillation. A typical heavy gas oil comprises a substantial portion of hydrocarbon components boiling above about 700xc2x0 F., usually at least about 50 percent by weight boiling above 700xc2x0 F. A typical vacuum gas oil normally has a boiling point range between about 600xc2x0 F. and about 1050xc2x0 F.
Hydrocracking is generally accomplished by contacting in a hydrocracking reaction vessel or zone the gas oil or other feedstock to be treated with a suitable hydrocracking catalyst under conditions of elevated temperature and pressure in the presence of hydrogen so as to yield a product containing a distribution of hydrocarbon products desired by the refiner. The operating conditions and the hydrocracking catalysts within a hydrocracking reactor influence the yield of the hydrocracked products.
Although a wide variety of process flow schemes, operating conditions and catalysts have been used in commercial activities, there is always a demand for new hydrocracking methods which provide lower costs and higher liquid product yields. It is generally known that enhanced product selectivity can be achieved at lower conversion per pass (60% to 90% conversion of fresh feed) through the catalytic hydrocracking zone. However, it was previously believed that any advantage of operating at below about 60% conversion per pass was negligible or would only see diminishing returns. Low conversion per pass is generally more expensive, however, the present invention greatly improves the economic benefits of a low conversion per pass process and demonstrates the unexpected advantages.
U.S. Pat. No. 5,720,872 discloses a process for hydroprocessing liquid feedstocks in two or more hydroprocessing stages which are in separate reaction vessels and wherein each reaction stage contains a bed of hydroprocessing catalyst. The liquid product from the first reaction stage is sent to a low pressure stripping stage and stripped of hydrogen sulfide, ammonia and other dissolved gases. The stripped product stream is then sent to the next downstream reaction stage, the product from which is also stripped of dissolved gases and sent to the next downstream reaction stage until the last reaction stage, the liquid product of which is stripped of dissolved gases and collected or passed on for further processing. The flow of treat gas is in a direction opposite the direction in which the reaction stages are staged for the flow of liquid. Each stripping stage is a separate stage, but all stages are contained in the same stripper vessel.
International Publication No. WO 97/38066 (PCT/US 97/04270) discloses a process for reverse staging in hydroprocessing reactor systems.
U.S. Pat. No. 3,328,290 (Hengstebeck) discloses a two-stage process for the hydrocracking of hydrocarbons in which the feed is pretreated in the first stage.
U.S. Pat. No. 5,114,562 (Haun et al) discloses a process wherein distillable petroleum streams are hydrotreated to produce a low sulfur and low aromatic product utilizing two reaction zones in series. The effluent of the first reaction zone is purged of hydrogen sulfide by hydrogen stripping and then reheated by indirect heat exchange. The second reaction zone employs a sulfur-sensitive noble metal hydrogenation catalyst.
U.S. Pat. No. 5,980,729 (Kalnes et al) discloses a hydrocracking process which utilizes a hot, high-pressure stripper.
U.S. Pat. No. 4,194,964 (Chen et al) discloses a process for the simultaneous distillation and hydrocracking of hydrocarbon feeds in a single vessel.
The present invention is a catalytic hydrocracking process which provides higher liquid product yields, specifically higher yields of turbine fuel and diesel oil. The process of the present invention provides the yield advantages associated with a low conversion per pass operation without compromising unit economics. Other benefits of a low conversion per pass operation include the minimization of the fresh feed pre-heat since the higher flow rate of recycle liquid will provide additional process heat to initiate the catalytic reaction and an additional heat sink to absorb the heat of reaction. The low conversion per pass operation requires less catalyst volume. An overall reduction in fuel gas and hydrogen consumption and light ends production may also be obtained.
The present invention utilizes a hydrogenation zone located in the lower end of the hot, high pressure separator to hydrogenate the downwardly flowing hydrocarbons in contact with upwardly flowing hydrogen. Since the downwardly flowing hydrocarbons passing through the hydrogenation zone have been stripped of hydrogen sulfide and ammonia, the hydrogenation is conducted in what is known as a sweet environment which is very favorable for the removal of relatively low levels of sulfur from the hydrocarbons. In addition, the upwardly flowing hydrogen effectively strips the produced hydrogen sulfide to produce ever increasingly lower sulfur hydrocarbons which are eventually removed from the bottom of the hot, high pressure separator. This resulting hydrocarbonaceous stream which is saturated with dissolved hydrogen and has a very low sulfur concentration, permits the use of catalysts in the hydrocracking zone which catalysts have superior performance characteristics. Therefore, the process of the present invention enables the use of high performance hydrocracking catalysts as well as the previously stated advantages.
In one embodiment the present invention relates to a, process for hydrocracking a hydrocarbonaceous feedstock to produce lower boiling hydrocarbonaceous compounds which process comprises: (a) contacting the hydrocarbonaceous feedstock, a liquid recycle stream having a temperature greater than about 500xc2x0 F. and saturated with hydrogen, and added hydrogen with a metal promoted hydrocracking catalyst in a hydrocracking zone at elevated temperature and pressure sufficient to obtain a substantial conversion to lower boiling hydrocarbons; (b) passing the hydrocracking zone effluent directly to a hot, high pressure stripper utilizing a hot, hydrogen-rich stripping gas to produce a first vapor stream comprising hydrogen, hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock, hydrogen sulfide and ammonia, and a downwardly flowing liquid comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock; (c) simultaneously contacting the downwardly flowing liquid in the hot, high pressure stripper with a hydrotreating catalyst and an upwardly flowing hydrogen stream to produce a first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock; (d) passing at least a portion of the first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock to the hydrocracking zone operating at a temperature from about 400xc2x0 F. to about 900xc2x0 F., a pressure from about 500 psig to about 2500 psig and a liquid hourly space velocity from about 0.1 hrxe2x88x921 to about 15 hrxe2x88x921; (e) condensing at least a portion of the first vapor stream comprising hydrogen, hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock, hydrogen sulfide and ammonia to produce a second liquid stream comprising hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock and a second vapor stream comprising hydrogen and hydrogen sulfide; and (f) passing at least a portion of the second vapor stream to the hydrocracking zone.
In another embodiment, the present invention relates to a process for hydrocracking a hydrocarbonaceous feedstock to produce lower boiling hydrocarbonaceous compounds which process comprises: (a) contacting the hydrocarbonaceous feedstock, a liquid recycle stream having a temperature greater than about 500xc2x0 F. and saturated with hydrogen, and added hydrogen with a metal promoted hydrocracking catalyst in a hydrocracking zone at elevated temperature and pressure sufficient to obtain a substantial conversion to lower boiling hydrocarbons; (b) passing the hydrocracking zone effluent directly to a hot, high pressure stripper utilizing a hot, hydrogen-rich stripping gas to produce a first vapor stream comprising hydrogen, hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock, hydrogen sulfide and ammonia, and a downwardly flowing liquid comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock; (c) simultaneously contacting the downwardly flowing liquid in the hot, high pressure stripper with a hydrotreating catalyst and an upwardly flowing hydrogen stream to produce a first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock; (d) passing at least a portion of the first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock to the hydrocracking zone operating at a temperature from about 400xc2x0 F. to about 900xc2x0 F., a pressure from about 500 psig to about 2500 psig and a liquid hourly space velocity from about 0.1 hrxe2x88x921 to about 15 hrxe2x88x921; (e) condensing at least a portion of the first vapor stream comprising hydrogen, hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock, hydrogen sulfide and ammonia to produce a second liquid stream comprising hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock and a second vapor stream comprising hydrogen and hydrogen sulfide; (f) passing at least a first portion of the second vapor stream to the hydrocracking zone; (g) introducing at least a second portion of the second vapor stream into a reflux heat exchange zone located in an upper end of the stripper to produce reflux; and (h) removing and heating the second portion of the second vapor stream from the reflux heat exchange zone and introducing the second portion of the second vapor stream into a lower end of the stripper to supply stripping medium and upwardly flowing hydrogen.
In yet another embodiment the present invention relates to a process for hydrocracking a hydrocarbonaceous feedstock to produce lower boiling hydrocarbonaceous compounds which process comprises: (a) contacting the hydrocarbonaceous feedstock, a liquid recycle stream having a temperature greater than about 500xc2x0 F. and saturated with hydrogen, and added hydrogen with a metal promoted hydrocracking catalyst in a hydrocracking zone at elevated temperature and pressure sufficient to obtain a substantial conversion to lower boiling hydrocarbons; (b) passing the hydrocracking zone effluent directly to a hot, high pressure stripper utilizing a hot, hydrogen-rich stripping gas to produce a first vapor stream comprising hydrogen, hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock, hydrogen sulfide and ammonia, and a downwardly flowing liquid comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock; (c) simultaneously contacting the downwardly flowing liquid in the hot, high pressure stripper with a hydrotreating catalyst and an upwardly flowing hydrogen stream to produce a first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock; (d) passing at least a portion of the first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock to the hydrocracking zone operating at a temperature from about 400xc2x0 F. to about 900xc2x0 F., a pressure from about 500 psig to about 2500 psig and a liquid hourly space velocity from about 0.1 hrxe2x88x921 to about 15 hrxe2x88x921; (e) passing at least a portion of the first vapor stream produced in step (b) to a post-treat hydrogenation reaction zone to saturate aromatic compounds; (f) condensing at least a portion of the resulting effluent from the post-treat hydrogenation reaction zone to produce a second liquid stream comprising hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock and a second vapor stream comprising hydrogen and hydrogen sulfide; and (g) passing at least a portion of the second vapor stream to the hydrocracking zone.
And further in another embodiment the present invention relates to a process for hydrocracking a hydrocarbonaceous feedstock to produce lower boiling hydrocarbonaceous compounds which process comprises: (a) contacting the hydrocarbonaceous feedstock, a liquid recycle stream having a temperature greater than about 500xc2x0 F. and saturated with hydrogen, and added hydrogen with a metal promoted hydrocracking catalyst in a hydrocracking zone at elevated temperature and pressure sufficient to obtain a substantial conversion to lower boiling hydrocarbons; (b) passing the hydrocracking zone effluent directly to a hot, high pressure stripper utilizing a hot, hydrogen-rich stripping gas to produce a first vapor stream comprising hydrogen, hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock, hydrogen sulfide and ammonia, and a downwardly flowing liquid comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock; (c) simultaneously contacting the downwardly flowing liquid in the hot, high pressure stripper with a hydrotreating catalyst and an upwardly flowing hydrogen stream to produce a first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock; (d) passing at least a portion of the first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock to the hydrocracking zone operating at a temperature from about 400xc2x0 F. to about 900xc2x0 F., a pressure from about 500 psig to about 2500 psig and a liquid hourly space velocity from about 0.1 hrxe2x88x921 to about 15 hrxe2x88x921; (e) passing at least a portion of the first vapor stream produced in step (b) to a post-treat hydrogenation reaction zone to saturate aromatic compounds; (f) condensing at least a portion of the resulting effluent from the post-treat hydrogenation reaction zone to produce a second liquid stream comprising hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock and a second vapor stream comprising hydrogen and hydrogen sulfide; (g) passing at least a portion of the second vapor stream to the hydrocracking zone; (h) introducing at least a second portion of the second vapor stream into a reflux heat exchanger located in an upper end of the stripper to produce reflux; and (i) removing and heating the second portion of the second vapor stream from the reflux heat exchange zone and introducing the second portion of the second vapor stream into a lower end of the stripper to supply stripping medium and upwardly flowing hydrogen.
In yet another embodiment, the present invention relates to a process for hydrocracking a hydrocarbonaceous feedstock to produce lower boiling hydrocarbonaceous compounds which process comprises: (a) contacting the hydrocarbonaceous feedstock, a liquid recycle stream having a temperature greater than about 500xc2x0 F. and saturated with hydrogen, and added hydrogen after hydrotreating with a metal promoted hydrocracking catalyst in a hydrocracking zone at elevated temperature and pressure sufficient to obtain a substantial conversion to lower boiling hydrocarbons; (b) passing the hydrocracking zone effluent directly to a hot, high pressure stripper utilizing a hot, hydrogen-rich stripping gas to produce a first vapor stream comprising hydrogen, hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock, hydrogen sulfide and ammonia, and a downwardly flowing liquid comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock; (c) simultaneously contacting the downwardly flowing liquid in the hot, high pressure stripper with a hydrotreating catalyst and an upwardly flowing hydrogen stream to produce a first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock; (d) passing at least a portion of the first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the hydrocarbonaceous feedstock to the hydrocracking zone operating at a temperature from about 400xc2x0 F. to about 900xc2x0 F., a pressure from about 500 psig to about 2500 psig and a liquid hourly space velocity from about 0.1 hrxe2x88x921 to about 15 hrxe2x88x921; (e) condensing at least a portion of the first vapor stream comprising hydrogen, hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock, hydrogen sulfide and ammonia to produce a second liquid stream comprising hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock and a second vapor stream comprising hydrogen and hydrogen sulfide; and (f) passing at least a portion of the second vapor stream to the hydrocracking zone.
Other embodiments of the present invention encompass further details such as types and descriptions of feedstocks, hydrocracking catalysts and preferred operating conditions including temperatures and pressures, all of which are hereinafter disclosed in the following discussion of each of these facets of the invention.